1. Field of the Invention
The present invention relates to a method and an apparatus for obtaining an image using a selective combination of light wavelengths. More particularly, the present invention relates to a method and an apparatus for obtaining an image using a selective combination of light wavelengths that can effectively obtain an image of an object, such as a stacked structure, using lights having selectively combined wavelength bands in accordance with the wavelength bands thereof.
2. Description of the Related Art
Generally, an apparatus for obtaining an image using light includes a light irradiation device for irradiating light onto an object and an imaging device like a camera for obtaining photographs of the object after the light is irradiated onto the object. The light irradiation device has a spectrometer for transmitting lights having desired wavelength bands according to a construction of the object.
FIG. 1 illustrates a schematic cross-sectional view of a conventional light irradiation device.
Referring to FIG. 1, a light irradiation device 20 includes a light source 21, such as a white LED, for emitting white light, a micro prism 22 for dispersing the white light 22a along a dispersion direction Y1, and a barrier 23 including a slit 23a for transmitting the light having predetermined wavelength bands among all the dispersed light. The slit 23a moves along the dispersion direction Y1 in order to transmit the light having changed wavelength bands or a width of the slit 23a is varied to transmit the light having varied wavelength bands.
FIG. 2 illustrates a schematic cross-sectional view of a conventional spectrometer.
Referring to FIG. 2, diffraction grids of a spectrometer 3 receive light reflected from a sample 2 after the light generated from a light source 1 is irradiated onto the sample 2. The spectrometer 3 disperses the light in a direction corresponding to wavelengths of the light. The dispersed light advances to a charge coupled device (CCD) line sensor 4 wherein minute light receiving devices are arranged. The CCD line sensor 4 includes a shutter 5 for electronically shielding light receiving faces thereof. A controller 7 generates shutter opening and closing signals Sc for controlling an opening period of the shutter 5 to adjust an amount of light received on the light receiving faces of the minute light receiving devices of the CCD line sensor 4.
An output signal Cd of the CCD line sensor 4 is received in a data processing member 10 through an A/D converter 6. The data processing member 10 includes a data memory section 11, a wavelength selecting section 12, a data selecting section 13, a compensating operator 14 and a spectrum generating section 15. The spectrometer 3 further includes an inputting member 16 and a display member 17 electrically connected to the data processing member 10.
FIG. 3 illustrates a schematic cross-sectional view of another conventional spectrometer.
Referring to FIG. 3, after light has passed through a slit 60, the light is converted into parallel light by a collimator 70. The parallel light is dispersed while the light passes through a prism 80. The dispersed light passes through a shutter 93 of a light modulator 90, and is incident upon a detecting member 100.
The above-mentioned apparatus for obtaining an image may be utilized in various fields. For example, the apparatus for obtaining an image may be employed to obtain images of patterns stacked on a wafer. The apparatus for obtaining an image primarily includes a light source emitting white light. However, a contrast ratio between images of the patterns obtained using the white light may be exceedingly low when a step between patterns formed on a wafer becomes minute as a planarization process is performed on the patterns on the wafer. More specifically, when the white light, which includes all wavelength bands, is irradiated onto the patterns to obtain the images of the patterns, reflection intensities of the light reflected from the patterns may be very low at all of the wavelength bands of the reflected light because of the minute step between the patterns. Hence, the images of the patterns may be hardly recognized.
In view of the above-mentioned problem, an apparatus including color filters disposed at light receiving portions thereof in order to select one filter wherein a wavelength band has a high contrast ratio among all of the wavelength bands of white light incident upon the color filters has been suggested. However, the selected wavelength band of the light may be fixed because one of the color filters should correspond to a predetermined wavelength band of the light. A contrast ratio between images of patterns generally depends on structures of the patterns and adjacent films. The wavelength band having the high contrast ratio may be varied according to this structure. Therefore, an image having a high contrast ratio may not be obtained using the color filters corresponding to the fixed wavelength bands.
Additionally, a method for obtaining an image by amplifying an image signal as a noise is reduced by taking an average of data numerals of obtained images after several images of an object are obtained has been suggested. However, this method may have a limitation in that the image signal may not be amplified to a certain degree. Thus, an image having a highest contrast ratio may not be obtained and a time for obtaining the image may be greatly increased because several images must be obtained.